> Flexible rings that fold up on themselves into saddle shapes or stacks of interlinked loops are most recognizable in such everyday items as pop-up tents and laundry baskets. A group of researchers led by Alain Jonas of the Catholic University of Leuven in Belgium has determined that the way these rings behave depends on a single characteristic known as overcurvature, or how much more curved the ring is than a flat circle of the same circumference.